lnvasive applications of echocardiography, including transesophageal echo, intravascular echo and intracardiac echo have been one of the most fertile areas driving new technology for ultraminiaturization and very high resolution. Among the most prolonged and detailed interventional catheterization procedures, electrophysiological mapping and ablation for recurrent atrial and ventricular arrhythmias have received recent attention because of the now-recognized need for spatial mapping in addition to fluoroscopic catheter localization, and because of the increased frequency of these debilitating rhythm problems in an aging population. We propose to design, develop and test a family of 2D and 3D ultrasound imaging devices which, at 10-15MHz operating frequency, will provide spatial localization, and both tissue velocity and strain rate estimates of mechanical activation in atrial and ventricular walls, to guide electrical mapping. This should greatly shorten time to localize critical areas. Our devices will be integrated with the EP electrode and RF ablation devices so that they can anatomically monitor the ablation procedure, visualize the lesion, and map the distribution of temperature during RF delivery focus. The devices we will build can also assess the heart before, during and after surgery as well as monitor anatomical catheter interventions for coronary artery, valvular or congenital heart disease. Our partnership is a multidisciplinary group of clinicians, surgeons, echocardiographers and electrophysiologists at OHSU, led by David J. Sahn, MD, Director of the Interdisciplinary Program For Cardiac Imaging, combined with bioengineers including: Matthew O'Donnell, PhD, Chair of the Department of Biomedical Engineering at the University of Michigan, Ann Arbor; Kirk Shung, PhD, director of an NIH Research Resource for Development of High Frequency Arrays at Pennsylvania State University, University Park; Kal Thomenius, PhD, Program Manager of Ultrasound Research at the General Electric Corporate Research and Development Center in Schenectady, New York; Douglas Stephens, Vice President of Strategic Technology at the Imaging Division of JOMED (formerly Endosonics Corporation) in Rancho Cordova, California, a pioneer in miniaturized array devices for intravascular and intracardiac imaging catheters; and Raymond Chia, PhD, of Irvine Biomedical, a small agile company with expertise in steerable multipolar electrode and ablation devices and their combination with other imaging modalities. The design and development of these devices combined with advanced functional imaging methods should open new vistas for applications in invasive echocardiography and ultrasound in general.